1. Field of the Invention
This invention relates to a method and an apparatus for controlling an air-fuel ratio and an ignition timing in an internal combustion engine, and more particularly to a method of and the apparatus for controlling an air-fuel ratio and an ignition timing in a steady running condition of spark-ignition engine.
2. Description of the Prior Art
In the spark-ignition engines in general, there has been used a three-way catalytic converter for purifying carbon monoxide, hydrocarbon and nitric oxide in the exhaust gas. To improve the rate of purification of this three-way catalytic converter, a fuel injection valve or a fuel injection nozzle is on-off controlled by a basic fuel injection pulse-width based on an engine rotational speed and an engine load (an intake pipe pressure or an intake air flowrate per turn of the engine), so that an air-fuel ratio of an air-fuel mixture can be controlled to be in the vicinity of a stoichiometric air-fuel ratio. Since a required ignition timing of the engine is varied depending upon the engine rotational speed and the engine load, the ignition timing is controlled so that the required ignition timing can be obtained depending upon the engine rotational speed and engine load.
In consequence, during the normal running condition excluding the case of a high load, the air-fuel ratio is controlled to be in the vicinity of the stoichiometric air-fuel ratio irrespective of an acceleration, a constant speed and a deceleration, and hence, the air-fuel ratio is not controlled to be one where the best fuel consumption rate can be attained in the conditions of running at a substantially constant speed.